Conversion with calibre changes text formatting

[ezeky]

I have an ebook in .mobi format with spaces after every paragraph. I used calibre to remove these spaces but the problem is that it changed text formatting too. In the original file there are lines which are written with uppercase letters but in the new one the letters are too small. I converted both versions to .epub and realized that calibre changed <span class="small"> to <span class="calibre8">. How can I solve this?
The other problem is that it removes spaces where it isn't necessary, i.e., after blocks of paragraphs, before those lines which start with word in uppercase letters.
For examples it becomes this:

Many people were beginning to come to similar conclusions.
CERTAINLY THE TRIP HAD NOT accomplished what his friends had hoped.

instead of this:

Many people were beginning to come to similar conclusions.

CERTAINLY THE TRIP HAD NOT accomplished what his friends had hoped.

This is also done to chapter titles.

[kovidgoyal]

http://manual.calibre-ebook.com/conv...size-rescaling

[ezeky]

Thank you very much for the answer! It's perfect now!